Multi-wavelength cross-connect optical switch

ABSTRACT

A cross-connect switch for fiber-optic communication networks employing a wavelength dispersive element, such as a grating, and a stack of regular (non-wavelength selective) cross bar switches using two-dimensional arrays of micromachined, electrically actuated, individually-tiltable, controlled deflection micro-mirrors for providing multiport switching capability for a plurality of wavelengths. Using a one-dimensional micromirror array, a fiber-optic based MEMS switched spectrometer that does not require mechanical motion of bulk components or large diode arrays can be constructed with readout capability for WDM network diagnosis or for general purpose spectroscopic applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/022,591filed on Feb. 12, 1998, now U.S. Pat. No. 6,097,859, which claimspriority from provisional application Ser. No. 60/038,172 filed on Feb.13, 1997.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO A MICROFICHE APPENDIX

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a cross-connect switch for fiber-opticcommunication networks including wavelength division multiplexed (WDM)networks, and more particularly to such an optical switch using a matrixof individually tiltable micro-mirrors.

2. Description of the Background Art

Multi-port, multi-wavelength cross-connect optical switches withcharacteristics of large cross-talk rejection and flat passband responsehave been desired for use in wavelength-division multiplexed (WDM)networks. Four-port multi-wavelength cross-bar switches based on theacousto-optic tunable filter have been described (“IntegratedAcoustically-tuned Optical Filters for Filtering and SwitchingApplications,” D. A. Smith, et al., IEEE Ultrasonics SymposiumProceedings, IEEE, New York, 1991, pp. 547-558), but they presentlysuffer from certain fundamental limitations including poor cross-talkrejection and an inability to be easily scaled to a larger number ofports. Attempts are being made to address to this problem by dilatingthe switch fabric, both in wavelength and in switch number, to provideimproved cross-talk rejection and to expand the number of switched portsso as to provide an add-drop capability to the 2×2 switch fabric. Thisstrategy, however, adds to switch complexity and cost. Recently, Pateland Silberberg disclosed a device employing compactly packaged,free-space optical paths that admit multiple WDM channels spatiallydifferentiated by gratings and lenses (“Liquid Crystal and Grating-BasedMultiple-Wavelength Cross-Connect Switch,” IEEE Photonics TechnologyLetters, Vol. 7, pp. 514-516, 1995). This device, however, is limited tofour (2×2) ports since it relies on the two-state nature of polarizedlight.

BRIEF SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide an improvedmulti-wavelength cross-connect optical switch which is scalable in portnumber beyond 2×2.

Another object of the invention to provide such an optical switch whichcan be produced by known technology.

Another object of this invention to provide such an optical switch withhigh performance characteristics such as basic low loss, high cross-talkrejection and flat passband characteristics.

Another object of the invention is to provide a fiber-optic switch usingtwo arrays of actuated mirrors to switch or rearrange signals from Ninput fibers onto N output fibers, where the number of fibers, N, can betwo, or substantially larger than 2.

Another object of the invention is to provide a fiber-optic switch using1-D arrays of actuated mirrors.

Another object of the invention is to provide a fiber-optic switch using2-D arrays of actuated mirrors.

Another object of the invention is to provide a fiber-optic switch usingmirror arrays (1-D or 2-D) fabricated using micromachining technology.

Another object of the invention is to provide a fiber-optic switch usingmirror arrays (1-D or 2-D) fabricated using polysilicon surfacemicromachining technology.

Another object of the invention is to provide a fiber-optic switch usingarrays (1-D or 2-D) of micromirrors suspended by torsion bars andfabricated using polysilicon surface micromachining technology.

Another object of the invention is to provide a fiber-optic switch withno lens or other beam forming or imaging optical device or systembetween the mirror arrays.

Another object of the invention is to provide a fiber-optic switch usingmacroscopic optical elements to image or position the optical beams fromthe input fibers onto the mirror arrays, and likewise using macroscopicoptical elements to image or position the optical beams from the mirrorarrays onto the output fibers.

Another object of the invention is to provide a fiber-optic switch usingmicrooptics to image or position the optical beams from the input fibersonto the mirror arrays, and likewise using microoptics to image orposition the optical beams from the mirror arrays onto the outputfibers.

Another object of the invention is to provide a fiber-optic switch usinga combination of macrooptics and microoptics to image or position theoptical beams from the input fibers onto the mirror arrays, and likewiseusing combination of macrooptics and microoptics to image or positionthe optical beams from the mirror arrays onto the output fibers.

Another object of invention is to provide a fiber-optic switch in whichthe components (fibers, gratings, lenses and mirror arrays) are combinedor integrated to a working switch using Silicon-Optical-Benchtechnology.

Another object of the invention is to provide a fiber-optic switch using2-D arrays of actuated mirrors and dispersive elements to switch orrearrange signals from N input fibers onto N output fibers in such afashion that the separate wavelength channels on each input fiber areswitched independently.

Another object of the invention is to provide a fiber-optic switch asdescribed above, using diffraction gratings as wavelength dispersiveelements.

Another object of the invention is to provide a fiber-optic switch asdescribed above, using micromachined diffraction gratings as wavelengthdispersive elements.

Another object of the invention is to provide a fiber-optic switch usingfiber Bragg gratings as wavelength dispersive elements.

Another object of the invention is to provide a fiber-optic switch usingprisms as wavelength dispersive elements.

Another object of the invention is to provide a fiber-optic based MEMSswitched spectrometer that does not require mechanical motion of bulkcomponents nor large diode arrays, with readout capability for WDMnetwork diagnosis.

Another object of the invention is to provide a fiber-optic based MEMSswitched spectrometer that does not require mechanical motion of bulkcomponents nor large diode arrays, with readout capability for generalpurpose spectroscopic applications.

Further objects and advantages of the invention will be brought out inthe following portions of the specification, wherein the detaileddescription is for the purpose of fully disclosing preferred embodimentsof the invention without placing limitations thereon.

An optical switch embodying this invention, with which the above andother objects can be accomplished, may be characterized as comprising awavelength dispersive element, such as a grating, and a stack of regular(non-wavelength selective) cross bar switches using a pair oftwo-dimensional arrays of micromachined, electrically actuated,controlled deflection micro-mirrors for providing multiport switchingcapability for a plurality of wavelengths.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood by reference to thefollowing drawings which are for illustrative purposes only:

FIG. 1 is a schematic diagram of an optical switch in accordance withthe present invention.

FIG. 2 is a schematic plan view of a single layer of the switchingmatrix portion of the optical switch shown in FIG. 1.

FIG. 3 is a diagrammatic plan view of a row of individually tiltablemicro-mirrors employed in the switch array portion of the optical switchshown in FIG. 1.

FIG. 4 is a schematic diagram showing switching matrix geometry inaccordance with the present invention.

FIG. 5 is a schematic sectional view of a grating made in silicon byanisotropic etching.

FIG. 6 is a schematic diagram of an alternative embodiment of theoptical switch shown in FIG. 1 employing a mirror in the symmetry plane.

FIG. 7 is a schematic plan view of a single layer of the switchingmatrix portion of the optical switch shown in FIG. 6.

FIG. 8 is a schematic diagram of a WDM spectrometer employing an opticalswitch in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring more specifically to the drawings, for illustrative purposesthe present invention is embodied in the apparatus generally shown inFIG. 1 through FIG. 8, where like reference numerals denote like parts.It will be appreciated that the apparatus may vary as to configurationand as to details of the parts without departing from the basic conceptsas disclosed herein.

Referring first to FIG. 1, a multi-pod (N×N ports), multi-wavelength (Mwavelength) WDM cross-connect switch 10 embodying this invention isschematically shown where, in the example shown, N=3. In this switch 10,the wavelength channels 12 a, 12 b, 12 c of three input fibers 14 a, 14b, 14 c are collimated and spatially dispersed by a first (or input)diffraction grating-lens system 16. The grating-lens system 16 separatesthe wavelength channels in a direction perpendicular to the plane of thepaper, and the dispersed wavelength channels are then focused onto acorresponding layer 18 a, 18 b, 18 c of a spatial micromechanicalswitching matrix 20. The spatially reorganized wavelength channels arefinally collimated and recombined by a second (or, output) diffractiongrating-lens system 22 onto three output fibers 24 a, 24 b, 24 c. Theinput and output lens systems are each composed of a lenslet array 26(32) and a pair of bulk lenses 28, 30 (34, 36) such that the spot sizeand the spot separation on the switching matrix 20 can be individuallycontrolled. Two quarter-wave plates 38, 40 are inserted symmetricallyaround the micromechanical switching matrix 20 to compensate for thepolarization sensitivity of the gratings 42, 44, respectively.

Referring now to FIG. 2, a schematic plan view of a single layer 18 a ofthe switching matrix 20 of FIG. 1 is shown. As can be seen in FIG, 2,six micromirrors 46 a through 46 f are arranged in two arrays 48 a, 48 bthat can be individually controlled so as to optically “couple” any ofthe three input fibers 14 a, 14 b, 14 c to any of the three outputfibers 24 a, 24 b, 24 c. Referring also to FIG. 3, an example of thestructural configuration of a row of individually tiltable micromirrorson the switch array can be seen. As shown in FIG. 3, each mirror 46 a,46 b, 46 c is suspended by a pair of torsion bars or flexing beams 50 a,50 b attached to posts 52 a, 52 b, respectively. Note that each mirroralso includes a landing electrode 54 on which the mirrors land when theyare deflected all the way down to the substrate.

The advantages of this switching matrix arrangement include low crosstalk because cross coupling between channels must go through twomirrors, both of which are set up to reject cross talk, low polarizationsensitivity, and scalability to larger numbers of input fibers than two(which is the limit for polarization-based switches). The preferredfabrication technology for the micromirror arrays is surfacemicromachining as disclosed, for example, in Journal of Vacuum Scienceand Technology B, Vol. 6, pp.1809-1813, 1988 because they can be made bythis method as small as the optical design will allow, they can bebatch-fabricated inexpensively, they can be integrated with on-chipmicromachinery from materials such as polysilicon and they can beminiaturized so as to reduce the cost of packaging.

Referring now to FIG. 4, there are several factors to consider fordesigning the switching matrix 20. FIG. 4 shows an example of two mirrorarrays 56 a, 56 b where each array comprises a plurality of mirrors, Nathrough Nn. The basic parameters are the Gaussian beam radium (ω_(o)) atthe center of the switch, the mirror size in the horizontal direction(s), the distance between the mirror arrays (p), the incident angle onthe mirror arrays (β), and the maximum deflection of the micromirrors(t). The maximum angular deflection (α) of the optical beams isdependent on the maximum deflection and the mirror size (in thehorizontal direction), or tan α=4t/s (the optical deflection being twicethat of the mechanical deflection and the mirrors being tethered attheir center points). Conditions that must be satisfied include: (i) theoptical beams must be sufficiently separated on the mirrors to keepcross-talk at reasonable levels; (ii) the sizes of the arrays must besmall enough such that no shadowing occurs; and (iii) the path lengthdifferences through the switch must not introduce significant variationsin insertion loss.

If a Gaussian-beam formalism is used, the cross coupling of two parallelbeams of radius ω_(o) offset by d is given as exp{−(d/ω_(o))2}. If thisshould be less than 40 dB, for example, the ratio C=d/ω_(o) must belarger than 3. This minimum ratio applies to both fiber-channel(horizontal) separation and wavelength channel (vertical) separation.Since the beam radii are larger at the mirrors due to diffraction thanat the focus, the above conclusion does not strictly apply, but it maybe required that the spacing of the beams must be at least three timeslarger than the optical beam radius also at the mirrors. Thisrequirement also reduces the losses due to aperture effects toinsignificant levels. The minimum mirror spacing (which is larger orequal to the mirror size) is then expressed as:

s=Cω/cosβ=C(ω_(o)/cosβ{1+(λp/2πω_(o) ²)²}^(1/2)

where C is a factor greater than 3, ω is the beam size at the mirrors,and λ is the wavelength of the light. This requirement, together withthe restrictions on angular deflection, puts an upper limit on thenumber of fiber channels (=N) in the switch. If the maximum deflectionangle is assumed small, the maximum number of channels is:

N=1+{4πcos β/C ² λ}t

The corresponding array separation and mirror spacing are:

p=2πω_(o) ²/λ

and

s=2^(1/2)Cω_(o)/cos β

If C=3, β=0.3 radian and λ=1.55 micron, N is given by N=1+0.86t where tis in micron. The conclusion is that the simple geometry of FIG. 4 canbe used to design relatively large switches. Using known surfacemicromachining techniques, switches with three fiber channels can befabricated with a total sacrificial layer thickness of 2.75 micron.Larger switching matrices will require thicker sacrificial layers, suchas 8.1 micron for N=8 and 17.4 micron for N=16. These thicknesses can beobtained by simply using thicker sacrificial layers or by usingout-of-plane structures, or through a combination of these.

The minimum beam radium ω_(o) is determined from the requirement thatthe first mirror array should not obstruct the beams after they arereflected from the second mirror, and that the second mirror arrayshould not obstruct the beams before they reach the second mirror. If Nis maximized, C=3, β=0.3 radian and λ=1.55 micron, the beam radium inmicron must be larger than the number of fiber channels, or ω_(o)>Nmicron. The requirement of maximum path length difference is lessrestrictive (ω_(o)>0.8(N−1) micron). In general, the mirrors should bemade as small as possible because miniaturization of the mirrors leadsto increased resonance frequencies, lower voltage requirements andbetter stability. For N=3, ω_(o) should preferably be on the order of 3micron, leading to a mirror spacing of s=13.3 micron. Mirrors of thissize, as well as mirrors suitable for larger matrices are easilyfabricated by a standard surface micromachining process. This impliesthat micromachined switching matrices can be scaled to large numbers offiber channels (e.g., N=16).

The minimum mirror separation in the wavelength-channel dimension may besmaller than the mirror separation s given above by the factor of cos βbecause the mirrors are not tilted in that direction. The spacing,however, may be larger because there is no switching in the wavelengthdirection and there is no maximum angle requirement. It may be preferredto add 20 to 30 micron of space between the mirrors for mirror posts(see FIG. 3) and addressing lines. For a switch with N=3 and s=110micron, for example, a preferred separation in the wavelength dimensionmay be on the order of 130 micron. If the Littrow configuration is used,the required size of the Gaussian-beam radium on the grating is:

ω_(g) =C _(w)λ²/2πΔλtanΘ_(c)

where C_(w) is the ratio of beam separation to beam radium in thewavelength dimension, Δλ is the wavelength separation between channelsand Θ_(c) is the incident angle (which equals the diffraction angle inthe Littrow configuration). With C_(w)=5.2 (25 micron beam radium and130 micron wavelength-channel separation), λ=1.55 micron, Δλ=1.6 nm(“the MONET standard”) and Θ_(c)=45 degrees, ω_(g) is 1.2 mm (the orderof diffraction m being 1). This means that the long side of the gratingperpendicular to the grooves must be on the order of 5.3 mm and thefocal length f₂ of the second lens (the one between the grating and themicroswitches) should be about 60.8 mm.

The rotation of the grating about an axis perpendicular to the opticalaxis and the grating grooves require a corresponding reduction of thegrating period by Λ=mλcos φ(2 sin Θ_(c)) where φ is the rotation angleof the grating. If m=1, λ=1.55 micron, Θ_(c)=45 degrees and φ=30degrees, the grating period is 0.95 micron.

In a simple system without the microlens arrays shown in FIG. 1, themagnification of the input plane onto the switching matrix is given bythe ratio of the focal length f₂ of the second lens to the focal lengthf₁ of the first lens (e.g., lens 28 between the lenslets 26 and grating42). The role of the lenslet is to allow a different magnification forthe mode size and for the mode spacing. In the optimized geometrydescribed above, the ratio of the mode separation to mode radius is2^(1/2)C=4.24. If the fibers are as close together as practicallypossible (e.g., 125 micron equal to the fiber diameter), the ratio onthe input is 125/5=25. The mode radius therefore must be magnified 5.9times more than the mode spacing. This can be accomplished in severalways.

According to one method, lenslets are used to magnify the fiber modeswithout changing the mode separation. The lenslets are placed less thanone focal length in front of the fibers to form an imaginary magnifiedimage of the fiber mode. Ideally, the lenslet diameters should becomparable to or smaller than the fiber diameter, allowing the minimumfiber separation and a short focal length of the first lens to bemaintained.

According to another method, the fiber mode is expanded adiabaticallyover the last part of its length by a heat treatment so as toout-diffuse the core. Mode size increase on the order of 4 times can beaccomplished.

According to still another method, the fibers are thinned down ormicroprisms are used to bring the modes closer together without changingthe mode size.

The first two methods require the same magnification or reduction of theinput field. The third method has the advantage that less reduction isneeded, leading to smaller systems. If N=3, ω_(o)=25 micron, s=110micronand f₂=60.8 mm, the required magnification is 0.84. If lenslets of 125micron diameter are used, the required focal length f₁ of the first lensis 72.4 mm. If lenslets of 200 micron diameter are used, the requiredmagnification is 0.525 and the required focal length f₁ of the firstlens is 115.8 mm.

Parameters of a switch according to one embodiment of this inventionwith three input channels and three output channels are summarized inTable 1.

Referring again to FIG. 3, the switching matrix design shown iscompatible with the MUMP (the Multiuser Micro Electro-Mechanical SystemProcess at the Microelectronics Center of North Carolina) and its designrules. The full switching matrix includes two arrays each with eightrows of the mirrors shown. The mirrors are actuated by an electrostaticfield applied between the mirror and an electrode underneath (notshown). Each of the mirrors in the switching matrix has three states,but the mirrors in the three rows do not operate identically. Thecentral mirror may send the beam to either side, while the outer mirrorsonly deflect to one side. According to one design, the two on the sidesare mirror images of each other, the center mirror being either in theflat state (no voltage applied) or brought down to the point where ittouches the substrate on either side. The electrode under the centralmirror is split in two to allow it to tilt either way. The side mirrorsalso have a state that is half way between the flat state and the fullypulled-down state. This may be achieved by having continuous controlover the mirror angles. Although this is complicated by theelectromechanical instability of parallel plate capacitors because, asthe voltage on the plates is increased, the capacitance goes up and thisleads to a spontaneous pulling down of the mirror when the voltage isincreased past a certain value, this effect can be avoided either bycontrolling the charge rather than the voltage on the capacitors, or byusing an electrode geometry that pushes the instability point past theangle to be accessed. Charge control utilizes the full range of motionof the mirrors but complicates the driver circuitry for the switch. Itmay be preferable to use electrode geometry to achieve the requirednumber of states.

When the MUMP process is used, the mirror size has a lower limit imposedby the minimum cross section that can be defined in this process. Toachieve large tilt angles without too much deflection of the rotationaxis of the mirror, the flexing beams must be kept short. The shorterthe flexing beam, the larger the mirrors must be for the electrostaticforce to be able to pull the mirrors down. Calculations show that thetwo side mirrors have the required angle when pulled down if use is madeof beams that are 15 to 20 micron long, depending on the exact value ofthe material constants. For the voltage requirement to be acceptable,the mirror size must be on the order of 100×100 micron. The beams of thecentral mirror may be slightly longer, the maximum angle for the centralmirror being half that of the side mirrors. The geometry as shown inFIG. 3 ensures that the side mirrors can be tilted to half their maximumangles before reaching the electrostatic instability. The correspondingresonance frequencies are on the order of 20 to 50 Khz. FIG. 3 shows oneof 8 layers of micromirrors in the switching matrix described above;that is, the mirrors are separated by 110 micron in the horizontal(fiber-channel) direction and by 130 micron in the vertical(wavelength-channel) direction. Two such arrays make up a switchingmatrix as shown in FIG. 2. The mirrors are shown on landing electrodes,that are shorted to the mirrors, when deflected all the way down to thesubstrate. Addressing lines and shorts are not shown in FIG. 3.

The whole switch may be fabricated in so-called silicon-optical benchtechnology. The lenses, the switching arrays and the in/out modules maybe integrated, but commercially available dielectric gratings are toobulky for this technology. Microgratings may be developed, based onanisotropic etching of silicon. Etching of the <100> surface of siliconthrough rectangular etch masks that are aligned with the [111]directionsof the substrate, creates V-shaped grooves defined by the <111>crystallographic planes of silicon. An array of such V-grooves 56constitutes a grating that can be used in the Littrow configuration asshown in FIG. 5. The spacing between grooves can be made arbitrarilysmall (e.g., 1 micron) by under-etching the mask and subsequentlyremoving this layer. The Littrow angle, which is determined by thecrystalline planes of silicon, is equal to 54.7 degrees. By takingadvantage of the well-defined shape of a unit cell of the grating, it ispossible to obtain high diffraction efficiency in higher orderdiffraction modes, the V-grooves constituting a blazed grating operatedon higher orders. Higher-order operation means that the wavelengthdependence of the diffraction efficiency increases. It can be shown thatwith 8 wavelengths separated by 1.6 nm centered at 1.55 micron and thegrating geometry of FIG. 5, the diffraction order can be increased tom=15 with less than 1% variation in the diffraction efficiency betweenwavelength channels. With m=15, λ=1.55 micron, Θ_(c)=54.7 degrees andφ=30 degrees, the grating period is calculated to be Λ=12.3 micron.V-grooves with this spacing can be easily patterned and etched by usingstandard micromachining technology. V-groove gratings fabricated in thisway can be metallized and used as gratings directly, or be used as amold for polysilicon microgratings that can be rotated out of the planeby using micro-hinges. A potentially very important additional advantageof higher-order gratings, as described here, is the reduced polarizationsensitivity as compared to first-order gratings. Since the periodicityis much larger than the wavelength, the diffraction will be close tobeing independent of polarization. Still, two wave plates may be used tocompensate for residual polarization sensitivity due to oblique anglereflections.

Referring now to FIG. 6 and FIG. 7, the fiber-optic switch, being,symmetric about its center, can be implemented with a symmetry mirror 58in the symmetry plane 60. This essentially cuts the component count inhalf. The output channels may either be on the input fibers andseparable by optical rotators (not shown) or on a separate output fiberarray (not shown) that is placed above the input array. In the lattercase, the micromirror array 62 and the symmetry mirror 58 are slightlytilted about an axis, such that the light is directed to the outputfiber array.

It will be appreciated that the fiber-optic switch of the presentinvention can serve network functions other than a traditional N×N×M(where M is the number of wavelengths in a WDM system).

It will further be appreciated that the fiber-optic switch of thepresent invention can be used in connection with diagnostic tools forWDM networks. WDM network management systems and software requireknowledge of the state of the entire network. Knowledge of the state ofthe many distributed optical channels is especially important. Themanager requires confirmation of whether or not a channel is active, itpower and how much a channel optical frequency has drifted as well asthe noise power level. Furthermore, this knowledge permits managementsoftware to identify, isolate, and potentially rectify or route aroundphysical layer faults.

Clearly network management requires numerous channel spectrometers thatmay be deployed in large number at affordable prices. Traditionally,such spectrometers are fabricated from gratings and lenses while anelectronically scanned diode array or a mechanically scanned gratingprovide spectral information. Unfortunately, diode array technology at1.55 microns, and 1.3 microns, the preferred communications wavelengths,is immature. Such arrays are much more costly and unreliable than thoseavailable for the visible spectral region. Moving gratings are bulky andcommercial system based on this approach are too costly for wide spreaduse in production networks.

Accordingly, a variation of the network switch described above can beemployed to provide the desired functionality. Referring to FIG. 8, anin-line WDM spectrometer 64 in accordance with the present invention isshown. In the embodiment shown in FIG. 8, WDM optical signals 66emanating from an input fiber 68 would be collimated and diffracted fromthe grating 70 forming a high resolution spatially dispersed spectrum atthe lens 72 focal plane. A single MEMS switch array 74 would be placedat the lens focal plane, thus permitting the deflection of individualoptical channels or portions of a channel by one or more mirrors in thearray. A quarter-wave plate 76 is inserted symmetrically around theswitching array 74 to compensate for the polarization sensitivity of thegratings 70. A single infrared diode detector 78 and focusing lens (notshown) would be placed in the return path of the reflected, and suitablydisplaced, return beam after a second grating diffraction from grating70. A full spectrum can then obtained by scanning a deflection acrossthe mirror array. Hence, a synchronized readout of the single photodiode yields the full spectrum to the management software.

The input fiber 68 and output fiber 80 can be arranged in a variety ofways. For example, they can be arranged side by side in the plane asshown in FIG. 8. An alternative would be to place the output fiber overor under the input fiber. A further alternative would be to use the samefiber for the input and output paths, and separate the signals using anoptical circulator or the like.

The micromirror array 74 is preferably a one-dimensional array with onemirror per wavelength. Each mirror would thus operate in one of twostates; the mirror either sends its corresponding wavelength to theoutput fiber 78 or is tilted (actuated) so that its correspondingwavelength is sent to the detector 76. In normal operation, only one ofthe mirrors is set up to deflect its wavelength to the detector.

Note also that, if the output fiber if removed and replaced by a beamsink (not shown), the spectrometer will still function although such anembodiment could not be used in an in-line application.

The invention has been described above by way of only a limited numberof examples, but the invention is not intended to be limited by theseexamples. Many modifications and variations, as well as design changesto significantly reduce the overall size, are possible within the scopeof this invention. For example, the beam radius in the switching matrixmay be reduced. The no-obstruction criterion allows a change to ω_(o)=5micron for a 4-fiber switch, and this allows the focal length of bothlenses to be reduced by a factor of 5. As another example, themicromachining technology may be improved to place the mirrors closer.The posts (as shown in FIG. 3) and addressing lines may be moved underthe mirrors to reduce the beam radium on the grating by a factor of 1.2.Together with the increased diffraction angle of a micromachine grating(say, to 54.7 degrees from 45 degrees), the focal lengths of the lensescan be reduced by a factor of 1.7. As a third example, the fiber modesmay be brought closer together on the in/out modules. If the modespacing is reduced from 200 micron to 22.2 micron, the first and secondlenses may have the same focal length (such that magnification =1). Inaddition, advanced designs may reduce the number of required components.The switch may be designed so as to be foldable about its symmetry pointsuch that the same lenses and the same grating will be used both on theinput and output sides. In summary, it is to be understood that all suchmodifications and variations that may be apparent to an ordinary personskilled in the art are intended to be within the scope of thisinvention.

Although the description above contains many specificities, these shouldnot be construed as limiting the scope of the invention but as merelyproviding illustrations of some of the presently preferred embodimentsof this invention. Thus the scope of this invention should be determinedby the appended claims and their legal equivalents.

TABLE 1 Components Parameter Values Input/output fibers Fiber channels:3 Standard single mode fiber Input-output MONET standard: wavelengthsCenter wavelength: 1.55 micron Wavelength channels: 8 Wavelengthseparation: 1.6 nm Lenslets Ball lens, 200-micron-diameter n < 1.6 Firstlens Bulk lens f₁ = 125.5 mm Grating Period: 0.95 micron Diffractionangle: 45 degrees Size: >6 mm Second Lens Bulk lens f₂ = 78.5 mmSwitching matrix N = 3 Mirror spacing: Fiber dimension: 110 micronWavelength dimension: 130 micron Array spacing: 2.5 mm Thickness ofsacrificial layer: 2.75 micron

What is claimed is:
 1. A fiber optic switch, comprising: (a) an inputarray of actuated mirrors; (b) an output array of actuated mirrors; (c)said mirrors configured for switching optic signals from a plurality ofinput optic fibers onto a plurality of output optic fibers; (d) whereinthe optical field from each specific input fiber is incident on onespecific mirror of the input array; (e) wherein each output fiberreceives an optical field from one specific mirror in the output array;(f) wherein each mirror of the input array can be set to steer theincident optical field to any, but not more than one for a given settingof the output mirrors; and (g) wherein each output mirror can be set toreceive an optical field from any, but not more than one for a givensetting, of the input mirrors.
 2. A fiber optic switch as recited inclaim 1, wherein separate wavelength channels on each input optic fiberare capable of being switched independently by said arrays of mirrors.3. A fiber optic switch as recited in claim 1, further comprising aplurality of optical elements for positioning optical beams from saidinput optic fibers onto said input array of mirrors.
 4. A fiber opticswitch as recited in claim 1, further comprising a plurality of opticalelements for positioning optical beams reflected from said output arrayof mirrors onto said output fibers.
 5. A fiber optic switch as recitedin claim 1, further comprising: (h) a wavelength dispersive element; and(i) a plurality of lenses associated with said wavelength dispersiveelement; (j) wherein said wavelength dispersive element and saidplurality of lenses are configured to position optical beams from saidinput optic fibers onto said input array of mirrors.
 6. A fiber opticswitch as recited in claim 5, wherein said wavelength dispersive elementcomprises a diffraction grating.
 7. A fiber optic switch as recited inclaim 5, further comprising: (k) a second wavelength dispersive element;and (l) a second plurality of lenses associated with said secondwavelength dispersive element; (m) wherein said second wavelengthdispersive element and said second plurality of lenses are configured toposition optical beams reflected by said output array of mirrors ontosaid output optic fibers.
 8. A fiber optic switch as recited in claim 7,wherein at least one of said wavelength dispersive elements comprises adiffraction grating.
 9. A fiber optic switch as recited in claim 1,wherein each of the mirrors in the input and output arrays can berotated around a single axis, with all axes of rotation being parallelsuch that the steered beams between the input and output arrays are allin a single plane.
 10. A fiber optic switch, comprising: (a) an inputarray of actuated mirrors; (b) an output array of actuated mirrors; (c)a first wavelength dispersive element; (d) a first plurality of lensesassociated with said first wavelength dispersive element; (e) a secondwavelength dispersive element; and (f) a second plurality of lensesassociated with said second wavelength dispersive element; (g) whereinsaid first wavelength dispersive element and said first plurality oflenses are configured to position optical beams from a plurality ofinput optic fibers onto said input array of mirrors and wherein saidsecond wavelength dispersive element and said second plurality of lensesare configured to position optical beams reflected by said output arrayof mirrors onto a plurality of output optic fibers.
 11. A fiber opticswitch as recited in claim 10, wherein separate wavelength channels oneach input optic fiber are capable of being switched independently bysaid arrays of mirrors.
 12. A fiber optic switch as recited in claim 10,wherein at least one of said wavelength dispersive elements comprises adiffraction grating.
 13. A fiber optic switch, comprising: (a) aplurality of input optic fibers; (b) a plurality of output optic fibers;(c) an input array of actuated mirrors; (d) an output array of actuatedmirrors; (e) a first wavelength dispersive element; (f) a firstplurality of lenses associated with said first wavelength dispersiveelement; (g) a second wavelength dispersive element; and (h) a secondplurality of lenses associated with said second wavelength dispersiveelement; (i) wherein said first wavelength dispersive element and saidfirst plurality of lenses are configured to position optical beams froma plurality of input optic fibers onto said input array of mirrors andwherein said second wavelength dispersive element and said secondplurality of lenses are configured to position optical beams reflectedby said output array of mirrors onto a plurality of output optic fibers.14. A fiber optic switch as recited in claim 13, wherein separatewavelength channels on each input optic fiber are capable of beingswitched independently by said arrays of mirrors.
 15. A fiber opticswitch as recited in claim 13, wherein at least one of said wavelengthdispersive elements comprises a diffraction grating.